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Human Development

Human Development. Biology 12. Joke of the day:. Sperm enters egg Resulting cell (egg + sperm) is called a zygote. Fertilization:. Ovulation to implantation:. Cleavage:. Occurs immediately after fertilization and splits the zygote into many smaller cells

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Human Development

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  1. Human Development Biology 12

  2. Joke of the day:

  3. Sperm enters egg Resulting cell (egg + sperm) is called a zygote Fertilization:

  4. Ovulation to implantation:

  5. Cleavage: • Occurs immediately after fertilization and splits the zygote into many smaller cells • Repeated mitotic divisions of zygote • Unequal divisions establishes body plan • different cells receive different portions of egg cytoplasm & therefore different regulatory signals

  6. Embryonic development • Day 1: 1st cleavage • 1 cell becomes 2 (2-cell stage) • Day 2: 2nd cleavage • 4-cell stage • Day 3: 6-12 cell stage • can test at this stage for genetic diseases if done by IVF • Day 4: 16-32 cell stage • solid ball of cells = morula

  7. Embryonic development • Day 5: • solid morula develops into hollow, fluid-filled blastula • embryo will develop from the inner cell mass, or embryonic disc • Day 6 -7: • blastocyst attaches to the endometrium and implantation occurs (now considered an embryo) *blastocyst starts to secrete HCG = human chorionic gonadotropin which stimulates estrogen & progesterone to prevent menstrual flow • pregnancy test measures the amount of this hormone!

  8. In pictures: zygote gastrulation blastula morula

  9. gastrulation • Embryo cell movements result in a massive reorganization of the embryo from a simple spherical ball of cells (blastula) into a multi-layered organism. • Many of the cells at or near the surface of the embryo move to a new, more interior location. • Days 7 to 10

  10. Gastrulation: • Establishes 3 cell layers • Ectoderm • outer body tissues • skin, nails, teeth • nerves, eyes, lining of mouth • Mesoderm • middle tissues • blood & lymph, bone & notochord, muscle • excretory & reproductive systems • Endoderm • inner lining • digestive system • lining of respiratory, excretory & reproductive systems ectoderm mesoderm endoderm

  11. Embryonic developmental Days 10 - 14: Pregnancy becomes established • Amnion (inner membrane)develops • Fluid filled amniotic cavity starts to form • Yolk sac starts to form (make blood cells, germ cells) • Placenta(site of exchange of nutrients and waste b/w mother and fetus) starts to form

  12. Neurulation • Formation of notochord & neural tube • develop into nervous system Neural tube develops into CNS (brain & spinal cord) Notochord develops intovertebral column

  13. Organogenesis • is the process by which the ectoderm, endoderm, and mesoderm develop into the internal organs of the organism. • Internal organs start development within the 3rd to 8th week

  14. Review: Embryonic Development Gastrulation Cleavage Ectoderm Mesoderm Endoderm Zygote 2-cell embryo Gastrula (cross section) Blastocyst (cross section) Morula

  15. Video: • Showing gastrulation, etc. • http://www.youtube.com/watch?v=UgT5rUQ9EmQ

  16. 4 weeks: • The organs begin to develop • The formation of the placenta, which is used for nutrition and waste removal • The formation of the amnion, which contains amniotic fluid for protection

  17. 4 week embryo showing tail & limb buds

  18. Week 5: beginning of the eye can be seen, as well the bulging heart & the umbilical cord

  19. Lens of the eye can be seen forming, the mass of the heart bulging from the chest, & the beginnings of the finger rays

  20. What’s next? • Embryo continues to grow and divide • After 8 weeks referred to as a fetus • Cells continue to differentiate (develop into specialized cells) • Fetus grows and develops • Born at ~40 weeks

  21. 8 weeks • Measures approximately the size of a bean • The tail disappears, turns into coccyx (tailbone) • Formation of the appendages, hands and joints • Formation of the tubes for the respiratory system. • Nervous system begins to form • Ossification (bone formation) begins

  22. 8 weeks: formation of the nose, eyelids, ear flap & well defined toes & fingers

  23. 12 weeks • Measures 5 cm • More developed eyes and ears • Kidneysbecome functional • More nervous system connections formed • The fetus can suck its thumb

  24. 16 weeks • Measures 10 cm and weighs 100g • Circulatory and urinary systems become functional • The heart beats strongly • The eyes begin to move • Toenails begin to grow

  25. 20 weeks • A waxy substance (vernix) coats the skin to provide protection from the amniotic fluid • The fetus is able to swallow • The production of meconium begins (digestive system)

  26. 24 weeks • Measures 30 cm and weighs 2 kg • Chance of survival if born now • The fetus is thin and begins to accumulate fat • The skin is thin and translucent • The formation of taste buds • The lungs continue to develop and are able to inflate due to the production of a fluid (pulmonary surfactant

  27. 24 weeks (6 months) • Fetus is covered with fine, downy hair called lanugo. • It’s skin is protected by a waxy substance called vernix

  28. Getting crowded in there!! • Growing, growing, growing……. • 32 weeks (8 months) The fetus sleeps 90-95% of the day & sometimes experiences REM sleep, an indication of dreaming

  29. 38 to 42weeks….Birth!

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